(1) Field of the Invention
This invention relates to an improved process for carpet manufacture. More particularly, this invention relates to an improved carpet manufacturing process employing a carboxylated styrene-butadiene rubber (SBR) adhesive whereby the improvement comprises forming a mixture of from 4% to 25% by dry weight saponified tall oil pitch and from 96% to 75% by dry weight carboxylated SBR to enhance the tack and final bond strength of the rubber adhesive. Fillers can also be included in the mixture as well as other ingredients.
(2) Description of the Prior Art
For many years the production of backsized tufted carpet has been accomplished by an aqueous latex method. This method involves preparing a tufted structure by stitching a primary backing material with yarn in such a manner as to form on the top surface of the material a pile composed of numerous closely spaced erect loops of fiber bundles, i.e., tufts of yarn. If desired, the loops can be cut. After forming the tufted structure, the bottom surface thereof is coated with a latex containing a polymer binder such as a styrene-butadiene copolymer and a secondary backing material is applied thereto. The structure is then passed through an oven to dry the latex. By such a process, the tufts of yarn and secondary backing material are bonded to the primary backing material. Also, the individual fiber filaments making up a fiber bundle are bonded together at the primary backing material.
The proccess of this invention may employ a latex foam backing in place of a secondary backing wherein the raw tufted carpet is pre-coated so that the latex is dried by passing through an oven prior to applying the foam to the underside, or latex coated side, of the carpet. After applying the foam backing, the carpet is passed again through a high temperature zone to cure the foam.
The foam backing may be applied via either the "gelled" or "no-gelled" systems. The gelled system includes in the foam formulation a gelling agent, such as ammonium acetate which, upon exposure to infrared heat, gels the foam for curing. Whereas, the no-gelled system does not contain a gelling agent. That system employs a surfactant which promotes excessive colloid stability which, in turn, maintains the foam during curing.
SBR has a relatively low polarity compared to other synthetic rubbers; and unlike natural rubber, SBR does not develop surface peroxidal activity upon mastication. Therefore, SBR has relatively poor inherent or processed tack. An adhesive is said to possess tack if, under the conditions of application, only light pressure is required to produce a bond sufficiently strong to require work to restore the interface to its original separated state. Poor tack in SBR can be overcome by: (1) reducing the molecular weight or changing the molecular weight distribution, (2) decreasing the viscosity with plasticizer or surface treating with solvent, or (3) adding tackifiers, such as resins or natural rubber.
It has been known for several years that incorporation of a very small percent of an unsaturated fatty acid monomer with styrene or styrene and butadiene improves the adhesive properties of the resulting polymer (i.e., Netherlands Application 6,411,493, Apr. 15, 1965--acrylic acid and fumaric acid and German Offenlegungschrift No. 2,437,365, Feb. 13, 1975--itaconic). Also, methacrylic and crotonic acids are suited to this purpose. In addition to improving adhesion, carboxylation provides reaction sites for cross-linking with curing agents to improve water resistance and improves processing properties. Thus, carboxylated polystyrene or styrene-butadiene rubber latex has been the backbone of many water-based adhesives for some time. Just as natural rubber is added to SBR to improve its tack (German Offenlegungschrift No. 2,005,244, Aug. 6, 1970), addition of natural rubber latex to the carboxylated latex increases the wet grab (green tack) of the adhesive system.
In the process described above, the tufted carpet industry depends on highly filled carboxylated styrene-butadiene rubber latex to simultaneously bond the carpet tufts to the primary backing through which they are punched and adhere a secondary backing or a foam backing to the bottom of the carpet. Due to the high cost of natural rubber latex, the natural latex gradually has been removed from this adhesive system. A typical composition is as follows:
______________________________________ Parts Dry Weight ______________________________________ Carboxylated SBR (45% to 60% styrene) 100 Filler 400 Antioxidant 1-2 Thickener 0.5 Water to adjust final solids ______________________________________
Adhesive solids are normally in the range of 70% to 85%. The filler portion of the formulation may contain more than one type. Whiting (calcium carbonate) is the most common filler. Certain systems contain alumina trihydrate (ATH) to meet the fire retardant standard.
With the carboxylated SBR latex alone, unaided by the natural latex, wet grab to the secondary backing is borderline. If the secondary backing separates from the carpet at any stage of drying, the final bond will never be as strong as if a coherent system were retained throughout the drying cycle. For this reason, the carpet industry, in particular, is interested in more economic methods of increasing the green tack of the carboxylated SBR adhesive, thereby enhancing the final bond of carpet to backing.
Therefore, it is an object of this invention to provide an improved carpet manufacturing process employing a carboxylated styrene-butadiene rubber adhesive wherein the improvement comprises replacing 4% to 25% of the rubber with saponified tall oil pitch to improve the bond of the carpet and primary and secondary backing materials. Another object of this invention is to provide an improved carpet manufacturing process wherein the green tack of the carboxylated styrene-butadiene rubber adhesive is improved. Still another object of this invention is to provide an improved process for carpet manufacture wherein the improvement comprises replacing 4% to 25% of carboxylated SBR with saponified tall oil pitch to increase the volume of the adhesive over the volume produced with carboxylated SBR alone, due to enhanced ability of the adhesive to incorporate air. The advantages obtained are good coverage at lower application weights and lower application cost per square yard (as air is used to extend the adhesive material).